1. Field of the Disclosure
The present invention relates to organic light emitting display devices, and more particularly to an organic light emitting display device which can prevent a light compensation layer from cracking; and a method for fabricating the same.
2. Discussion of the Related Art
An image display device which realizes various pieces of information is a core technology of an information and communication times and developing in a direction of high performance while thinner, lighter, and portable. Recently, as a bendable flexible display is in demand owing to pursuance of spatial convenience, the organic light emitting display device is spot lighted, in which a light emitting quantity of an organic light emitting layer thereof is controlled by a flat display device.
The organic light emitting display device has a thin film transistor array on a substrate, an organic light emitting display element on the thin film transistor array, and a glass cap for isolating the organic light emitting display device from an external environment. The organic light emitting display device uses electroluminescence in which a light is emitted by coupling energy of an electron and a hole. If an electric field is applied to a cathode and an anode formed on both ends of an organic light emitting layer, the electron and the hole are injected and transmitted to the organic light emitting layer, and the electron and the hole which form a pair in the organic light emitting layer drops from an excited state to a base state to emit the light.
In detail, the organic light emitting display device is provided with sub-pixels disposed at every region defined as gate lines GL and data lines DL cross. Each of the sub-pixels receives a data signal supplied through the data line DL whenever a gate pulse is supplied to the gate line GL to emit the light corresponding to the data signal.
FIG. 1 illustrates a circuit diagram of a related art organic light emitting display device, and FIG. 2 illustrates a photograph of a light compensating layer having a crack taken place therein.
Referring to FIG. 1, each of the sub-pixels has an organic light emitting element EL having a cathode connected to a ground voltage source GND, and a cell drive unit 152 connected to a gate line GL, a data line DL, and a supply voltage source VDD as well as an anode of the organic light emitting element EL for driving the organic light emitting element EL. The cell drive unit 152 has a switching thin film transistor T1, a drive thin film transistor T2, and a capacitor C.
The switching thin film transistor T1 is turned on when a scan pulse is supplied to the gate line GL to supply a data signal supplied to a data line DL to a first node N1. The data signal supplied to the first node N1 is charged to the capacitor C, and supplied to a gate terminal of the drive thin film transistor T2. The drive thin film transistor T2 controls a current being supplied to the organic light emitting element EL from the supply voltage source VDD in response to the data signal supplied to the gate terminal to control a light emitting quantity of the organic light emitting element EL.
And, since the capacitor C discharges the data signal even if the switching thin film transistor T1 is turned off, the drive thin film transistor T2 supplies the current from the supply voltage source VDD to the organic light emitting element EL to sustain the light emission from the organic light emitting element EL until a next frame data signal is supplied.
The drive thin film transistor has an active layer with a source region, a channel region, and a drain region, a gate electrode overlapped with the channel region of the active layer with a gate insulating film disposed therebetween, a source electrode connected to the source region insulated from the gate electrode with an interlayer insulating film disposed therebetween, and a drain electrode connected to the drain region. There are a protective layer formed on the interlayer insulating film including the source and drain electrodes, and a color filter formed on the protective layer. There are a planarizing layer formed on the protective layer including the color filter, and the organic light emitting element formed on the planarizing layer in contact with the drain electrode exposed by selective removal of the protective layer and the planarizing layer.
In the meantime, if the organic light emitting display device is a white organic light emitting display device which emits a white light, since the white color is produced by mixing red, green and blue R, G, B color filters, light emitting quantities of the red color, the green color and the blue color R, G, B vary depending upon an angle of view, causing color shift to drop a display quality.
Consequently, in order to prevent the color shift from taking place, the white organic light emitting display device has a light compensating layer formed of an inorganic material on the planarizing layer. However, stress is generated at a boundary of the light compensating layer and the planarizing layer due to a difference of thermal expansive coefficients between the light compensating layer and the planarizing layer to cause a crack at the light compensating layer, as shown in FIG. 2. In this case, an anode formed on the light compensating layer is broken, dropping reliability of the organic light emitting display device.